WebDAV SEARCH

This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026.¶

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1This document specifies a set of methods, headers, properties and content-types composing WebDAV SEARCH, an application of the HTTP/1.1 protocol to efficiently search for DAV resources based upon a set of client-supplied criteria.¶

2Distribution of this document is unlimited. Please send comments to the Distributed Authoring and Versioning (WebDAV) DASL working group at www-webdav-dasl@w3.org, which may be joined by sending a message with subject "subscribe" to www-webdav-dasl-request@w3.org.

5This document defines WebDAV SEARCH, an application of HTTP/1.1 forming a lightweight search protocol to transport queries and result sets and allows clients to make use of server-side search facilities. It is based on the expired draft for WebDAV DASL [DASL]. [DASLREQ] describes the motivation for DASL.¶

6DASL will minimize the complexity of clients so as to facilitate widespread deployment of applications capable of utilizing the DASL search mechanisms.¶

17The augmented BNF used by this document to describe protocol elements is exactly the same as the one described in Section 2.1 of [RFC2616]. Because this augmented BNF uses the basic production rules provided in Section 2.2 of [RFC2616], those rules apply to this document as well.¶

18The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT" "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].¶

19When an XML element type in the "DAV:" namespace is referenced in this document outside of the context of an XML fragment, the string "DAV:" will be prefixed to the element type.¶

20Note that this draft currently defines elements and properties in the WebDAV namespace "DAV:", which it shouldn't do as it isn't a work item of the WebDAV working group. The reason for this is the desire for some kind of backward compatibility to the expired DASL drafts and the assumption that the draft may become an official RFC submission of the WebDAV working group at a later point of time.¶

21Similarily, when an XML element type in the namespace "http://www.w3.org/2001/XMLSchema" is referenced in this document outside of the context of an XML fragment, the string "xs:" will be prefixed to the element type.¶

30The Request-URI identifies the search arbiter. Any HTTP resource may function as search arbiter. It is not a new type of resource (in the sense of DAV:resourcetype as defined in [RFC2518]), nor does it have to be a WebDAV-compliant resource.¶

31The SEARCH method defines no relationship between the arbiter and the scope of the search, rather the particular query grammar used in the query defines the relationship. For example, the FOO query grammar may force the request-URI to correspond exactly to the search scope.¶

32The server MUST process a text/xml or application/xml request body, and MAY process request bodies in other formats. See [RFC3023] for guidance on packaging XML in requests.¶

33If the client sends a text/xml or application/xml body, it MUST include the DAV:searchrequest XML element. The DAV:searchrequest XML element identifies the query grammar, defines the criteria, the result record, and any other details needed to perform the search.¶

34The DAV:searchrequest XML element contains a single XML element that defines the query. The name of the query element defines the type of the query. The value of that element defines the query itself.¶

35If the server returns 207 (Multistatus), then the search proceeded successfully and the response MUST match that of a PROPFIND. The results of this method SHOULD NOT be cached.¶

36There MUST be one DAV:response for each resource that matched the search criteria. For each such response, the DAV:href element contains the URI of the resource, and the response MUST include a DAV:propstat element.¶

37In addition, the server MAY include DAV:response items in the reply where the DAV:href element contains a URI that is not a matching resource, e.g. that of a scope or the query arbiter. Each such response item MUST NOT contain a DAV:propstat element, and MUST contain a DAV:status element (unless no property was selected).¶

38A response MAY include more information than PROPFIND defines so long as the extra information does not invalidate the PROPFIND response. Query grammars SHOULD define how the response matches the PROPFIND response.¶

39This example demonstrates the request and response framework. The following XML document shows a simple (hypothetical) natural language query. The name of the query element is natural-language-query in the XML namespace "http://example.com/foo". The actual query is "Find the locations of good Thai restaurants in Los Angeles". For this hypothetical query, the arbiter returns two properties for each selected resource.¶

42A server MAY limit the number of resources in a reply, for example to limit the amount of resources expended in processing a query. If it does so, the reply MUST use status code 207, return a DAV:multistatus response body and indicate a status of 507 (Insufficient Storage) for the search arbiter URI. It SHOULD include the partial results.¶

I believe the same response body that
contains the first N <DAV:response> elements should also contain a
*different* element stating that the results were incomplete and the result
set was truncated by the server.
There may also be a need to report that the results were incomplete and the
result set was truncated at the choice of the client (isn't there a limit
set in the client request?) That's important so the client knows the
difference between receiving 10 results because there were >10 but only 10
were asked for, and receiving 10 results because there were only exactly 10
results and it just happens that 10 were asked for.

I agree that this could be useful, but I think this issue should be
consolidated with issue JW5 (see below), which proposes that DASL
basicsearch ought to have a way for client to request additional result
sets. It should be moved because there is little or no value in allowing a
client to distinguish between the case where "N results were requested, and
there are exactly N available" and "N results were requested, and there are
more than N available" if there is no way for client to get the next batch
of results.

43When a result set is truncated, there may be many more resources that satisfy the search criteria but that were not examined.¶

44If partial results are included and the client requested an ordered result set in the original request, then any partial results that are returned MUST be ordered as the client directed.¶

45Note that the partial results returned MAY be any subset of the result set that would have satisfied the original query.¶

48If an error occurred that prevented execution of the query, the server MUST indicate the failure with the appropriate status code and SHOULD include a DAV:multistatus element to point out errors associated with scopes.¶

49400 Bad Request. The query could not be executed. The request may be malformed (not valid XML for example). Additionally, this can be used for invalid scopes and search redirections.¶

50422 Unprocessable entity. The query could not be executed. If a application/xml or text/xml request entity was provided, then it may have been well-formed but may have contained an unsupported or unimplemented query operator.¶

51A client may submit a scope that the arbiter may be unable to query. The inability to query may be due to network failure, administrative policy, security, etc. This raises the condition described as an "invalid scope".¶

52To indicate an invalid scope, the server MUST respond with a 400 (Bad Request).¶

53The response includes a body with a DAV:multistatus element. Each DAV:response in the DAV:multistatus identifies a scope. To indicate that this scope is the source of the error, the server MUST include the DAV:scopeerror element.¶

55Servers MUST support discovery of the query grammars supported by a search arbiter resource.¶

56Clients can determine which query grammars are supported by an arbiter by invoking OPTIONS on the search arbiter. If the resource supports SEARCH, then the DASL response header will appear in the response. The DASL response header lists the supported grammars.¶

65The DASL response header indicates server support for a query grammar in the OPTIONS method. The value is a URI that indicates the type of grammar. Note that although the URI can be used to identify each supported search grammar, there is not necessarily a direct relationship between the URI and the XML element name that can be used in XML based SEARCH requests (the element name itself is identified by it's namespace name (a URI reference) and the element's local name).¶

72This example shows that the server supports search on the /somefolder resource with the query grammars: DAV:basicsearch, http://foo.bar.com/syntax1 and http://akuma.com/syntax2. Note that every server MUST support DAV:basicsearch.¶

79Servers MAY support the discovery of the schema for a query grammar.¶

80The DASL response header and the DAV:supported-query-grammar-set property provide provides means for clients to discover the set of query grammars supported by a resource. This alone is not sufficient information for a client to generate a query. For example, the DAV:basicsearch grammar defines a set of queries consisting of a set of operators applied to a set of properties and values, but the grammar itself does not specify which properties may be used in the query. QSD for the DAV:basicsearch grammar allows a client to discover the set of properties that are searchable, selectable, and sortable. Moreover, although the DAV:basicsearch grammar defines a minimal set of operators, it is possible that a resource might support additional operators in a query. For example, a resource might support a optional operator that can be used to express content-based queries in a proprietary syntax. QSD allows a client to discover these operators and their syntax. The set of discoverable quantities will differ from grammar to grammar, but each grammar can define a means for a client to discover what can be discovered.¶

81In general, the schema for a given query grammar depends on both the resource (the arbiter) and the scope. A given resource might have access to one set of properties for one potential scope, and another set for a different scope. For example, consider a server able to search two distinct collections, one holding cooking recipes, the other design documents for nuclear weapons. While both collections might support properties such as author, title, and date, the first might also define properties such as calories and preparation time, while the second defined properties such as yield and applicable patents. Two distinct arbiters indexing the same collection might also have access to different properties. For example, the recipe collection mentioned above might also indexed by a value-added server that also stored the names of chefs who had tested the recipe. Note also that the available query schema might also depend on other factors, such as the identity of the principal conducting the search, but these factors are not exposed in this protocol.¶

82Each query grammar supported by DASL defines its own syntax for expressing the possible query schema. A client retrieves the schema for a given query grammar on an arbiter resource with a given scope by invoking the SEARCH method on that arbiter, with that grammar and scope, with a query whose DAV:select element includes the DAV:queryschema property. This property is defined only in the context of such a search, a server SHOULD not treat it as defined in the context of a PROPFIND on the scope. The content of this property is an XML element whose name and syntax depend upon the grammar, and whose value may (and likely will) vary depending upon the grammar, arbiter, and scope.

87Each query grammar supported by DASL defines its own syntax for expressing the possible query schema. A client retrieves the schema for a given query grammar on an arbiter resource with a given scope by invoking the SEARCH method on that arbiter with that grammar and scope and with a root element of DAV:query-schema-discovery rather than DAV:searchrequest.

97DAV:basicsearch uses an extensible XML syntax that allows clients to express search requests that are generally useful for WebDAV scenarios. DASL-extended servers MUST accept this grammar, and MAY accept others grammars.¶

The purpose is to allow one to express queries more precisely, e.g. to distinguish between the English word "hoop" (a circular object) and Dutch "hoop" (hope). Imagine a property that holds keywords for a resource. See 4.4 in http://www.ietf.org/rfc/rfc2518.txt, and 2.12 in http://www.w3.org/TR/REC-xml

I think this would be an interesting feature, but it seems to be extremely hard to implement.
So assuming a query that
- the query specifies a language and
- be the text content of the property matches
The result will be:
1) true (match), if the property was stored with a matching xml:lang property (where the language tag matching rules would have to apply)
2) undefined if the property was stored without xml:lang
3) false otherwise
On the other hand if
- the query doesn't specify a language
the result will be:
4) undefined (at least according to the current wording).
So,
1) requires that the query engine actually knows how to match language tags -- I'm not sure that everybody is willing to implement that.
2) is this desirable?
3) ok.
4) that seems to be wrong. If the query doesn't care, it should match, right?
Other problems:
- what is the language of a date-typed property?
- (sic!) where should xml:lang go into the query? There's no XML feature to undefine an xml:lang which is in scope, but there may be cases where this is needed.
On the other hand, if we drop this requirement, a client can still do a query and then process the result set -- the property elements in the response body will be reported with xml:lang (when persisted with language) anyway.
So I'd recommend to drop the feature. Defining string comparisons vs. collation sequences is hard enough.

106DAV:select defines the result record, which is a set of properties and values. This document defines two possible values: DAV:allprop and DAV:prop, both defined in [RFC2518].¶

107If the value is DAV:allprop, the result record for a given resource includes all the properties for that resource.¶

108If the value is DAV:prop, then the result record for a given resource includes only those properties named by the DAV:prop element. Each property named by the DAV:prop element must be referenced in the Multistatus response.¶

109The rules governing the status codes for each property match those of the PROPFIND method defined in [RFC2518].¶

112When the scope is a collection, if DAV:depth is "0", the search includes only the collection. When it is "1", the search includes the (toplevel) members of the collection. When it is "infinity", the search includes all recursive members of the collection.¶

116Servers, of course, may support only particular scopes. This may include limitations for particular schemes such as "http:" or "ftp:" or certain URI namespaces.¶

117If a scope is given that is not supported the server MUST respond with a 400 status code that includes a Multistatus error. A scope in the query appears as a resource in the response and must include an appropriate status code indicating its validity with respect to the search arbiter.¶

119This example shows the response if there is a scope error. The response provides a Multistatus with a status for the scope. In this case, the scope cannot be reached because the server cannot search another server (502).¶

120DAV:where element defines the search condition for inclusion of resources in the result set. The value of this element is an XML element that defines a search operator that evaluates to one of the Boolean truth values TRUE, FALSE, or UNKNOWN. The search operator contained by DAV:where may itself contain and evaluate additional search operators as operands, which in turn may contain and evaluate additional search operators as operands, etc. recursively.¶

DAV:href isn't a property, so
it can't be used in queries. Is this a problem? Examples where DAV:displayname
is queried instead seem to indicate that. A possible solution would be
to allow DAV:href whereever DAV:prop is allowed in the where clause.

121Each operator defined for use in the where clause that returns a Boolean value MUST evaluate to TRUE, FALSE, or UNKNOWN. The resource under scan is included as a member of the result set if and only if the search condition evaluates to TRUE.¶

122Consult Appendix A for details on the application of three-valued logic in query expressions.¶

130The example shows a more complex operation involving several operators (DAV:and, DAV:eq, DAV:gt) applied in the criteria. This DAV:where expression matches those resources that are "image/gifs" over 4K in size.¶

131The DAV:orderby element specifies the ordering of the result set. It contains one or more DAV:order elements, each of which specifies a comparison between two items in the result set. Informally, a comparison specifies a test that determines whether one resource appears before another in the result set. Comparisons are applied in the order they occur in the DAV:orderby element, earlier comparisons being more significant.¶

132The comparisons defined here use only a single property from each resource, compared using the same ordering as the DAV:lt operator (ascending) or DAV:gt operator (descending). If neither direction is specified, the default is DAV:ascending.¶

In the WebDAV SEARCH spec (5.6, DAV:orderby), it says that nulls sort
low, to match SQL92.
However, SQL92 and SQL99 both say "Whether a sort key value that is
null is
considered greater or less than a non-null value is
implementation-defined,
but all sort key values that are null shall either be considered
greater than
all non-null values or be considered less than all non-null values."
(words taken from SQL99, 14.1 <declare cursor> General Rule 2)c), in
reference to null handling for the <order by clause>. )
I would note that in 5.5.3 WebDAV SEARCH says nulls are less than all
other values in a comparison, so the DAV:orderby matches that
statement,
it just gives an inaccurate reason.

133In the context of the DAV:orderby element, null values are considered to collate before any actual (i.e., non null) value, including strings of zero length ( as in [SQL99]).¶

XPath/XQuery (see draft,
and open issue)
specify string comparisons based on collations, not languages. I think we should
adopt this. This would mean that "xml:lang" would be removed, and an optional
attribute specifying the name of the collation is added.

134Comparisons on strings take into account the language defined for that property. Clients MAY specify the language using the xml:lang attribute. If no language is specified either by the client or defined for that property by the server or if a comparison is performed on strings of two different languages, the results are undefined.¶

135The DAV:casesensitive"casesensitive" attribute may be used to indicate case-sensitivity for comparisons. Servers SHOULD do caseless matching as defined in [CaseMap].¶

Define how comparisons on strings work, esp for i18n.
Need policy statement about sort order in various national languages. (JW said "non-Latin" but it's an issue even in languages that use the latin char set.)

142The DAV:lt, DAV:lte, DAV:gt, and DAV:gte operators provide comparisons on property values, using less-than, less-than or equal, greater-than, and greater-than or equal respectively. The DAV:casesensitive"casesensitive" attribute may be used with these elements.¶

The current DASL draft doesn't really have Booleans or any other data type.
It's trying to skate on data types. Booleans could be tested using the "eq"
and the combination "not eq", if you had well defined literals for TRUE and
FALSE. With the current syntax, that is the way you would have to test a
Boolean. Generally, Boolean values are not considered to be ordered, so "gt"
etc. wouldn't apply. However, if the literal values of a Boolean were 1 and
0 for TRUE and FALSE (using the most commonly used convention of positive
logic), then you would have an obvious ordering. 1 and 0 have the advantage
of being language independent. You now see a lot of electronic and
electro-mechanical devices (air conditioners, computers, etc.) with a "1/0"
label on the power switch, "1" meaning "on", and "0" meaning "off".
SQL databases don't have Booleans. SQL doesn't control DASL, of course, but
SQL databases are so widely used that they are important. The closest thing
in SQL is a bit field. Each bit in a bit field is zero or 1.
So, why not close the issue by saying: DASL doesn't have data types. You can
simulate Booleans by an integer data type, using 1 for "TRUE" and 0 for
"FALSE".

144White space in literal values is significant in comparisons. For consistency with [RFC2518], clients SHOULD NOT specify the attribute "xml:space" (section 2.10 of [XML]) to override this behaviour.¶

146Rationale: This operator is provided in lieu of defining generic structure queries, which would suffice for this and for many more powerful queries, but seems inappropriate to standardize at this time.¶

5.13 should discuss handling of queries when character set differs.
Some text on handling character sets would be helpful.

160The DAV:contains operator is an optional operator that provides content-based search capability. This operator implicitly searches against the text content of a resource, not against content of properties. The DAV:contains operator is intentionally not overly constrained, in order to allow the server to do the best job it can in performing the search.¶

161The DAV:contains operator evaluates to a Boolean value. It evaluates to TRUE if the content of the resource satisfies the search. Otherwise, It evaluates to FALSE.¶

162Within the DAV:contains XML element, the client provides a phrase: a single word or whitespace delimited sequence of words. Servers MAY ignore punctuation in a phrase. Case-sensitivity is left to the server.¶

163The following things may or may not be done as part of the search: Phonetic methods such as "soundex" may or may not be used. Word stemming may or may not be performed. Thesaurus expansion of words may or may not be done. Right or left truncation may or may not be performed. The search may be case insensitive or case sensitive. The word or words may or may not be interpreted as names. Multiple words may or may not be required to be adjacent or "near" each other. Multiple words may or may not be required to occur in the same order. Multiple words may or may not be treated as a phrase. The search may or may not be interpreted as a request to find documents "similar" to the string operand.¶

164The DAV:score property is intended to be useful to rank documents satisfying the DAV:contains operator.¶

On the topic of partial search results, DASL currently has no way
for a client to request the next chunk of a set of search results.
Since *every* search service I've interacted with on the Internet
has a feature for returning the next set of search results, I really
would expect this feature to be in DASL. An explanation for why this
feature isn't present should be in the protocol specification if it
is not going to be supported.

of course this issue is legitim. However, as basicsearch should be as simple
as possible, I tend to say out of scope as well. But perhaps this could be
an optional feature (is it that, what you mean by extension to
DAV:basicsearch)?

171The possible values for DAV:casesensitive are "1" or "0". The "1" value indicates case-sensitivity. The "0" value indicates case-insensitivity. The default value is server-specified. Case-insensitivity SHOULD implemented using caseless matching as defined in [CaseMap].

172Support for the DAV:casesensitive is optional. A server should respond with an error 422 if the DAV:casesensitive attribute is used but cannot be supported.

174The possible values for "casesensitive" are "1" or "0". The "1" value indicates case-sensitivity. The "0" value indicates case-insensitivity. The default value is server-specified. Case-insensitivity SHOULD implemented using caseless matching as defined in [CaseMap].

175Support for the "casesensitive" attribute is optional. A server should respond with a status of 422 if it is used but cannot be supported.

176The DAV:score XML element is a synthetic property whose value is defined only in the context of a query result where the server computes a score, e.g. based on relevance. It may be used in DAV:select or DAV:orderby elements. Servers SHOULD support this property. The value is a string representing the score, an integer from zero to 10000 inclusive, where a higher value indicates a higher score (e.g. more relevant).¶

177Clients should note that, in general, it is not meaningful to compare the numeric values of scores from two different query results unless both were executed by the same underlying search system on the same collection of resources.¶

178The DAV:basicsearch grammar defines a search criteria that is a Boolean-valued expression, and allows for an arbitrary set of properties to be included in the result record. The result set may be sorted on a set of property values. Accordingly the DTD for schema discovery for this grammar allows the server to express:¶

the set of properties that may be either searched, returned, or used to sort, and a hint about the data type of such properties

184Each instance of a DAV:propdesc element describes the property or properties in the DAV:prop element it contains. All subsequent elements are descriptions that apply to those properties. All descriptions are optional and may appear in any order. Servers SHOULD support all the descriptions defined here, and MAY define others.¶

185DASL defines five descriptions. The first, DAV:datatype, provides a hint about the type of the property value, and may be useful to a user interface prompting for a value. The remaining four (DAV:searchable, DAV:selectable, DAV:sortable, and DAV:casesensitive) identify portions of the query (DAV:where, DAV:select, and DAV:orderby, respectively). If a property has a description for a section, then the server MUST allow the property to be used in that section. These descriptions are optional. If a property does not have such a description, or is not described at all, then the server MAY still allow the property to be used in the corresponding section.¶

186This element can be used in place of DAV:prop to describe properties of WebDAV properties not mentioned in any other DAV:prop element. For instance, this can be used to indicate that all other properties are searchable and selectable without giving details about their types (a typical scenario for dead properties).¶

187The DAV:datatype element contains a single XML element that provides a hint about the domain of the property, which may be useful to a user interface prompting for a value to be used in a query. Datatypes are identified by an element name. Where appropriate, a server SHOULD use the simple datatypes defined in [XS2].¶

190If this element is present, then the server MUST allow this property to appear within a DAV:where element where an operator allows a property. Allowing a search does not mean that the property is guaranteed to be defined on every resource in the scope, it only indicates the server's willingness to check.¶

193This element only applies to properties whose data type is "xs:string" and derived data types as per the DAV:datatype property description. Its presence indicates that compares performed for searches, and the comparisons for ordering results on the string property will be case sensitive. (The default is case insensitive.)¶

194The DAV:operators element describes every optional operator supported in a query. (Mandatory operators are not listed since they are mandatory and permit no variation in syntax.). All optional operators that are supported MUST be listed in the DAV:operators element. The listing for an operator consists of the operator (as an empty element), followed by one element for each operand. The operand MUST be either DAV:operand-property or DAV:operand-literal, which indicate that the operand in the corresponding position is a property or a literal value, respectively. If an operator is polymorphic (allows more than one operand syntax) then each permitted syntax MUST be listed separately.¶

195This response lists four properties. The datatype of the last three properties is not given, so it defaults to xs:string. All are selectable, and the first three may be searched. All but the last may be used in a sort. Of the optional DAV operators, DAV:isdefined and DAV:like are supported.¶

196Note: The schema discovery defined here does not provide for discovery of supported values of the DAV:casesensitive"casesensitive" attribute. This may require that the reply also list the mandatory operators.¶

197Clients have the opportunity to tag properties when they are stored in a language. The server SHOULD read this language-tagging by examining the xml:lang attribute on any properties stored on a resource.¶

200This section is provided to detail issues concerning security implications of which DASL applications need to be aware. All of the security considerations of HTTP/1.1 also apply to DASL. In addition, this section will include security risks inherent in searching and retrieval of resource properties and content.¶

201A query must not allow one to retrieve information about values or existence of properties that one could not obtain via PROPFIND. (e.g. by use in DAV:orderby, or in expressions on properties.)¶

202A server should prepare for denial of service attacks. For example a client may issue a query for which the result set is expensive to calculate or transmit because many resources match or must be evaluated. 7.1 Implications of XML External Entities¶

203XML supports a facility known as "external entities", defined in section 4.2.2 of [XML], which instruct an XML processor to retrieve and perform an inline include of XML located at a particular URI. An external XML entity can be used to append or modify the document type declaration (DTD) associated with an XML document. An external XML entity can also be used to include XML within the content of an XML document. For non-validating XML, such as the XML used in this specification, including an external XML entity is not required by [XML]. However, [XML] does state that an XML processor may, at its discretion, include the external XML entity.¶

204External XML entities have no inherent trustworthiness and are subject to all the attacks that are endemic to any HTTP GET request. Furthermore, it is possible for an external XML entity to modify the DTD, and hence affect the final form of an XML document, in the worst case significantly modifying its semantics, or exposing the XML processor to the security risks discussed in [RFC3023]. Therefore, implementers must be aware that external XML entities should be treated as untrustworthy.¶

205There is also the scalability risk that would accompany a widely deployed application which made use of external XML entities. In this situation, it is possible that there would be significant numbers of requests for one external XML entity, potentially overloading any server which fields requests for the resource containing the external XML entity.¶

217ANSI standard three valued logic is undoubtedly the most widely practiced method of dealing with the issues of properties in the search condition not having a value (e.g., being null or not defined) for the resource under scan, and with undefined expressions in the search condition (e.g., division by zero, etc.). Three valued logic works as follows.¶

218Undefined expressions are expressions for which the value of the expression is not defined. Undefined expressions are a completely separate concept >from the truth value UNKNOWN, which is, in fact, well defined. Property names and literal constants are considered expressions for purposes of this section. If a property in the current resource under scan has not been set to a value (either because the property is not defined for the current resource, or because it is null for the current resource), then the value of that property is undefined for the resource under scan. DASL 1.0 has no arithmetic division operator, but if it did, division by zero would be an undefined arithmetic expression.¶

219If any subpart of an arithmetic, string, or datetime subexpression is undefined, the whole arithmetic, string, or datetime subexpression is undefined.¶

221Since a Boolean value is ultimately returned by the search condition, arithmetic, string, and datetime expressions are always arguments to other operators. Examples of operators that convert arithmetic, string, and datetime expressions to Boolean values are the six relational operators ("greater than", "less than", "equals", etc.). If either or both operands of a relational operator have undefined values, then the relational operator evaluates to UNKNOWN. Otherwise, the relational operator evaluates to TRUE or FALSE, depending upon the outcome of the comparison.¶

222The Boolean operators DAV:and, DAV:or and DAV:not are evaluated according to the following rules:¶

moved data types before change history rewrote the data types section removed the casesensitive element and replace with the casesensitive attribute added the casesensitive attribute to the DTD for all operations that might work on a string

Jul 20, 1998

A series of changes. See Author's meeting minutes for details.

July 28, 1998

Changes as per author's meeting. QSD uses SEARCH, not PROPFIND. Moved text around to keep concepts nearby. Boolean literals are 1 and 0, not T and F. contains changed to contentspassthrough. Renamed rank to score.

Removed redirection feature, since 301/302 suffices. Removed Query Schema Discovery (former chapter 4). Everyone agrees this is a useful feature, but it is apparently too difficult to define at this time, and it is not essential for DASL.

Removed "xml:space" feature on DAV:literal. Added issue about string comparison vs. collations vs. xml:lang. Updated some of the open issues with details from JimW's original mail in April 1999. Resolved scope vs relative URI references. Resolved issues about DAV:ascending (added to index) and the BNF for DAV:like (changed "octets" to "characters").

Closed open issues regaring the type of search arbiters (JW3) and their discovery (JW9). Rephrased requirements on multistatus response bodies (propstat only if properties were selected, removed requirement for responsedescription).

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